A polycarbonate resin is generally produced by using bisphenols as a monomer component and is widely utilized as a so-called engineering plastic in the fields of electric/electronic parts, automotive parts, medical parts, building materials, films, sheets, bottles, optical recording mediums, lenses, etc. by taking advantage of its superiority such as transparency, heat resistance and mechanical strength. In addition, a polycarbonate diol is utilized as a raw material of polyurethane, etc., for example, by reacting it with an isocyanate compound.
However, a conventional polycarbonate resin causes deterioration in hue, transparency and mechanical strength when it is used in a place exposed to ultraviolet ray or visible light for a long time, and its usage at outdoors or near a lighting unit is therefore limited.
In order to solve such a problem, a method of adding a benzophenone-based ultraviolet absorber, a benzotriazole-based ultraviolet absorber, or a benzoxazine-based ultraviolet absorber to a polycarbonate resin is widely known (for example, Non-Patent Document 1).
However, addition of such an ultraviolet absorber poses a problem, for example, causes the resin to deteriorate in its original hue, heat resistance and transparency or to volatilize during molding and contaminate the mold, although the hue, etc. after ultraviolet irradiation may be improved.
The bisphenol compound used for a conventional polycarbonate resin has a benzene ring structure and therefore shows a large ultraviolet absorption, and this leads to deterioration in light resistance of the polycarbonate resin.
It is expected that when an aliphatic or alicyclic dihydroxy compound having no benzene ring structure in the molecular framework or a cyclic dihydroxy compound having an ether bond in the molecule, such as isosorbide, is used for a raw material monomer, the light resistance is improved in principle. Among others, a polycarbonate resin produced by using, as a raw material monomer, isosorbide obtained from biomass resources has excellent heat resistance and mechanical strength, and from the viewpoint of effective utilization of non-exhaustible resources as well, many investigations are being made thereon in recent years (for example, Patent Documents 1 to 5).
As for the polycarbonate resin using only isosorbide, a resin having such high heat resistance that the glass transition temperature (hereinafter, sometimes simply referred to as Tg) exceeds 160° C. is obtained (Patent Document 5). However, this polycarbonate resin has a drawback in that the impact resistance is low and the water absorptivity is high. In order to solve these problems, it has been proposed to achieve improvement by copolymerizing an aliphatic dihydroxy compound or an alicyclic dihydroxy compound (Patent Documents 1 to 4). However, copolymerization with such a dihydroxy compound produces a dilemma in that not only the heat resistance is sacrificed but also the utilization of biomass resources declines.
Inositol is a cyclic polyhydric alcohol obtained from biomass resources and is expected to form a polymer when coupled with a compound reacting with a hydroxy group. Non-Patent Documents 2 and 3 have reported that when a polyurethane was synthesized from an inositol derivative, the heat resistance was enhanced.
A polyurethane is obtained by reacting a polyhydric alcohol and a diisocyanate under relatively mild conditions of 100° C. or less and has no problem in reacting even with a compound having a secondary hydroxyl group, such as inositol derivative. However, it is generally known that an aliphatic dihydroxy compound having a secondary hydroxyl group is reduced in the polymerization reactivity due to its low acidity and steric hindrance and hardly provides a high-molecular-weight polycarbonate resin (Non-Patent Document 4).
Furthermore, in the case of a polyurethane, not only a tri- or higher functional structure, if any, does not become a serious problem but also the heat resistance can be enhanced by positively forming a network (Non-Patent Document 3). On the other hand, in the case of a thermoplastic resin typified by a polycarbonate resin, there is a problem that when a tri- or higher functional structure is coupled, gelling proceeds and gives rise to an insoluble matter or a defect.